Long-term unattended electric power sources allow various loads to be powered for great lengths of time without the necessity of replacing any of the components. Some long-term power sources may be a power supply that includes an arrangement of various components such as energy sources, energy storage devices, and power converters. These components are arranged such that the energy sources provide power to both the load and to the energy storage devices for storage, which allow the energy storage devices to supply power to the load if the energy sources are unavailable. Allowing interconnection of a number of power supplies would increase both the storage capacity and load capacity. However, the challenge exists to control the interconnected power supplies to ensure that individual power supplies charge and discharge uniformly. Many systems attempting to achieve this to date require the use of a master controller or peer-to-peer communication among the interconnected power supplies. Other attempts have implemented methods such as a “democratic sharing” in which a conventional voltage mode controller includes an extra term to compensate for the difference between the output current of a particular power supply and the average output current of all of the interconnected power converters.